(9) Standard operating procedures for making
stream and wet weather conveyance determinations (hydrologic determinations).
(a) General.
1. Because a primary purpose of the Water
Quality Control Act is to protect the waters of the state for the public, and
since streams receive a higher level of protection than wet weather
conveyances, anyone desiring to alter a watercourse who wishes to avoid
unnecessary expense and delay, may request the department to process a permit
application or issue an authorization under a general permit with the
presumption that the watercourse is a stream. In that instance, a full
hydrologic determination would not be performed under these rules. However,
nothing shall preclude an applicant from subsequently seeking a wet weather
conveyance determination.
2. The
procedures detailed in this rule are intended to be used in situations where
there is some question whether a watercourse is a stream or wet weather
conveyance. In situations where it is obvious that a watercourse is a stream,
such as named rivers or streams with watersheds larger than a square mile, or
spring-fed streams with consistent flow greater than one cubic foot per second,
it is not necessary to conduct a detailed hydrologic determination.
3. It is the purpose of this rule to set out
the framework for making stream and wet weather conveyance determinations
taking into consideration all relevant and necessary information on the
biology, geology, geomorphology, precipitation, hydrology, and other
scientifically based principles. Staff of the Department and certified
hydrologic professionals not employed by the Department who are making a
submission pursuant to T.C.A. §
69-3-108(r) shall
follow these rules and the Guidance for Making Hydrologic Determinations
(Guidance) which contains the instructions and examples for proper application
of these rules to situations in the field that has been developed pursuant to
T.C.A. §
69-3-107(25) in
making these determinations.
4. The
format for documenting these determinations is provided in the Hydrologic
Determination Field Data Sheet (Data Sheet) in the Guidance. All available
field characteristics necessary to make an accurate determination shall be
evaluated, and all evidence utilized in making a determination shall be
documented using the Data Sheet or as an addendum. Applicants may choose to
submit additional hydrological or geotechnical data not included in the
standard procedure in support of a hydrologic determination. Any additional
relevant information submitted to the Department shall be considered by the
Division in its determination.
5.
Any significant revision to the Data Sheet or Guidance shall be subject to a
30-day public comment period prior to adoption. The Department shall advertise
its intent to modify the Data Sheet or Guidance by posting notice of proposed
changes on the Department's internet web site and by sending to the permit
mailing list. Significant modifications include the addition or deletion or
substantive modification of either the primary or secondary indicators or a
change in the scoring system. The Department shall consider the need for
modifications to the Data Sheet and Guidance periodically and whenever a
significant comment is submitted in regard to them.
6. To be classified as a wet weather
conveyance, a watercourse must meet all four elements of the definition in
T.C.A. §
69-3-103. Therefore, if it is
determined that any one of the four elements does not apply to a watercourse,
the watercourse is a stream.
7.
Because natural variation and human activities can alter hydrologic conditions
over time, hydrologic determination will only be considered valid for a maximum
of five years or the term of a permit based on it.
8. Because there can be considerable
variability within a given reach of a watercourse, wet weather conveyance
determinations should not be made on a single point but must also investigate
up and down channel and consider the watercourse's landscape context.
9. All of the indicators referred to in these
rules and the Guidance are evidence relevant to the presence or absence of one
or more of the four elements of the wet weather conveyance definition. The
difference between the primary and secondary indicators is that each of the
primary indicators is considered presumptive evidence alone regarding one or
more of the four elements, and will allow for an immediate hydrologic
determination to be made in most cases. Some of the primary indicators involve
direct observations of the presence or absence of one or more of the elements.
The primary indicators of wet weather conveyances are:
(i) Hydrologic feature exists solely due to a
process discharge;
(ii) Defined bed
and bank absent, watercourse dominated by upland vegetation/grass;
(iii) Watercourse dry anytime during February
through April 15 under normal precipitation/groundwater conditions;
and
(iv) Daily flow and
precipitation records showing feature only flows in direct response to
rainfall.
10. Primary
indicators of streams are:
(i) Presence of
multiple populations of obligate lotic organisms with two months or longer
aquatic phase;
(ii) Presence of
fish (except Gambusia);
(iii)
Presence of naturally occurring groundwater table connection;
(iv) Flowing water in channel seven days or
more since the last precipitation in the local watershed; and
(v) Evidence watercourse has been used as a
supply of drinking water.
11. When primary indicators cannot be
observed or documented, then the investigator must evaluate the watercourse
using secondary indicators. The secondary indicators are an aggregate set of
observations that in total are used to evaluate the presence or absence of one
or more of the elements of a wet weather conveyance. Secondary indicators are:
(i) Continuous bed and bank;
(ii) Sinuous channel;
(iii) In-channel structure, riffle-pool
sequences;
(iv) Sorting of soil
textures or other substrate;
(v)
Active/relic floodplain;
(vi)
Depositional bars or benches;
(vii)
Braided channel;
(viii) Recent
alluvial deposits;
(ix) Natural
levees;
(x) Headcuts;
(xi) Grade controls;
(xii) Natural valley drainageway;
(xiii) At least second order channel on
United States Geological Survey or Natural Resources Conservation Service
map;
(xiv) Subsurface
flow/discharge into channel;
(xv)
Water in channel more than forty-eight hours since rain;
(xvi) Leaf litter in channel;
(xvii) Sediment on plants or on
debris;
(xviii) Organic debris
lines or piles (wrack lines);
(xix)
Hydric soils in channel bed or sides;
(xx) Fibrous roots in channel;
(xxi) Rooted plants in channel;
(xxii) Crayfish in channel (exclude in
floodplain);
(xxiii)
Bivalves/mussels;
(xxiv)
Amphibians;
(xxv)
Macrobenthos;
(xxvi) Filamentous
algae, periphyton;
(xxvii)
Iron-oxidizing bacteria/fungus; and
(xxviii) Wetland plants in channel.
12. The secondary indicators shall
be scored in accordance with the instructions in the Guidance. Hydrologic
determinations will often be made on the basis of secondary indicators because
none of the primary indicators are present at the time of investigation. Any of
the primary indicators contained in these rules and the Guidance may be
considered conclusive after consideration of appropriate background information
including recent weather and precipitation, in the absence of any directly
contradictory evidence. However, since hydrologic determinations are required
to be made at all times of year, secondary indicators of hydrologic status will
be used, in accordance with the Guidance and these rules, as determinant
evidence in the absence of primary indicators. The secondary indicators used in
the Guidance shall be based on sound scientific principles.
13. Watercourses in which flow is solely a
result of process or wastewater discharge or other non-natural sources shall
not be regulated as streams even though they may exhibit characteristics of a
stream rather than a wet weather conveyance.
(b) The specific procedures outlined herein
are intended to consider each of the four elements necessary for a watercourse
to be classified as a wet weather conveyance.
1. Because the duration of the flow in a
watercourse is the central inquiry of hydrologic determinations, all of the
primary and secondary indicators are relevant to evaluating it. Although other
factors may also be relevant, at a minimum the following procedures shall be
used to determine if a watercourse flows only in direct response to
precipitation runoff in its immediate vicinity.
(i) Prior to conducting a field evaluation,
the investigator should review recent precipitation patterns for the local
area, the longer-term seasonal precipitation trends, and any other available
information such as historic land use, regional geology and soil types, or
previous hydrologic determinations near the site to be investigated.
(ii) The investigator must decide if the
determination is being conducted under "normal weather conditions." The
procedure for determining if weather conditions are normal, or either wetter or
drier than normal, is contained in the Guidance. If conditions are either
wetter or drier than normal the investigator must take this into consideration
in making a hydrologic determination.
(iii) The vast majority of wet weather
conveyances will generally cease to flow within 48 hours of almost all except
some of the largest rain events. This is especially true in urbanized,
impervious areas, or other areas with low infiltration rates, such as mowed
lawns. The investigator shall document the presence or absence of flow within
the watercourse. If in-stream surface flow is observed within the evaluated
reach, and it has been at least seven days since the last rainfall event in the
upstream watershed, the flow will not be considered a direct storm response,
and the investigator shall conclude that the feature is a stream. The
investigator shall document the source of the precipitation data. The source
used shall be as close as feasible to the watercourse.
(iv) When subsurface water discharges such as
seeps, interstitial flow, perched water, or interflow are observed and used as
indicators of hydrology, investigators shall consider the influence of recent
precipitation events and localized soil and geologic conditions on these
features to determine if these features provide adequate hydrology such that
the watercourse flows more than in direct response to precipitation. For
example, since some such features have more flow when there has been
significant recent precipitation, if they are flowing when there has not been
much recent precipitation, it is more likely that they flow for sustained
periods. In some instances, there may be observable outcroppings of a confining
layer such as shale or clay that causes interstitial flow to discharge to a
watercourse. In this situation, the capacity of up-gradient conditions such as
the permeability and volume of the soils above the confining layer to sustain
extended periods of surface flow should be considered. These types of sustained
discharges should not be considered a direct response to rainfall. In other
instances, such as in areas with a highly karst geology, observed seeps into a
watercourse may be not be able to sustain extended periods of flow, and may be
considered a more direct response to rainfall.
(v) Field investigations for hydrologic
determinations should not be conducted if a one-inch precipitation event in 24
hours has occurred in the area of investigation within the previous 48
hours.
2. The following
procedures are to determine if the channel is above the groundwater table at
all times. Under the definition of wet weather conveyance in T.C.A. §
69-3-103, if there are any times
that the channel is not above the groundwater table, it is a stream.
(i) Since larger streams and rivers are
frequently in contact with the groundwater table, the investigator shall review
topographic maps to determine if the watercourse is within the floodplain of,
or within 20 feet in elevation of a larger stream or river known to carry
perennial flow. Flow in such a watercourse should not be considered conclusive
evidence of a groundwater table connection, but is contributing evidence to be
considered in the determination. Therefore further investigation into
additional factors including those listed below is necessary to determine that
the watercourse in question is in contact with the groundwater table.
(ii) Since the presence of wetlands often
indicates a shallow depth to the groundwater table, the investigator shall
search for the presence of wetlands in the immediate vicinity of the
watercourse both on topographic maps and in the field. The presence of wetlands
in the vicinity of the watercourse being examined should not be considered
conclusive evidence of a groundwater table connection, but is contributing
evidence to be considered in the determination. Therefore further investigation
into other factors including those listed below is necessary to determine that
the watercourse in question is in contact with the groundwater table.
(iii) The investigator shall review United
States Department of Agriculture soil surveys. Their soil descriptions often
contain information on depth to water table. For watercourses whose channels
are at a depth that indicates contact with the groundwater table for the soil
type in which they are formed, the investigator can conclude that the
watercourse is in contact with the water table, absent contradicting field
information.
(iv) The investigator
shall review site geological characteristics affecting the elevation of the
groundwater table with respect to the elevation of the channel, including the
presence of karst bedrock features, erodibility of watershed soils, thickness
of regolith and channel alluvium, depth to bedrock or laterally persistent silt
or clay horizons, land-use disturbances, and other watershed conditions
controlling or contributing to the presence or absence of channel base
flow.
(v) If data are available
from water wells within one mile of and in similar landscape position to a
watercourse under investigation, and if the surface elevation of standing water
in the well is at or above the elevation of the bottom of the channel of the
watercourse, then the investigator can conclude that the watercourse is in
contact with the groundwater table.
(vi) The observed emergence of water from the
ground is not necessarily water from the groundwater table and should not be
considered as conclusive for the purpose of this element. Therefore further
investigation into factors including those listed above is necessary to
determine the source of the emergent water.
3. The following procedures are to determine
if a watercourse is suitable for drinking water supplies. The investigator
should note spring boxes, water pipes to carry water from the watercourse to a
residence, or other observable evidence the watercourse is being used as a
household water supply upstream of or within the segment being evaluated. When
these features are noted, the investigator can conclude that the watercourse is
a stream absent contradicting information.
4. The following procedures are to determine
if a watercourse, under normal weather conditions, due to naturally occurring
ephemeral or low flow does not have sufficient water to support fish, or
multiple populations of obligate lotic aquatic organisms whose life cycle
includes an aquatic phase of at least two months.
(i) The presence of the requisite aquatic
life is a primary indicator that the watercourse supports that aquatic life. In
order to find that the requisite aquatic life is present, the investigator must
document more than one individual of at least two qualifying taxa in the
evaluated reach under normal weather conditions. Unhatched eggs or any other
stage of a taxon's life cycle that could be found in a wet weather conveyance
or lentic habitat (such as a deceased winged adult) should not be considered as
a primary indicator that a watercourse is a stream. The specific taxa found
should be noted on the Data Sheet. Representative individuals of the taxa used
to make this determination should be collected for confirmation of
identification. All aquatic life observed should be noted, even if some do not
qualify as primary indicators. These organisms may also be relevant as
secondary field indicators.
(ii)
Indigenous members of taxa within the benthic macroinvertebrate groups listed
below are obligate lotic aquatic organisms and thus are primary indicators that
a watercourse is a stream when two or more specimens of two or more taxa are
documented under normal weather conditions.
(I) Gastropoda: Pleuroceridae, Viviparidae,
Valvatidae
(II) Bivalvia:
Unionidae
(III) Coleoptera:
Dryopidae, Elmidae, Psephenidae, Ptilodactylidae, Staphylinidae
(IV) Diptera: Athericidae, Blephariceridae,
Chironomidae (except: Chironomini or red midges), Empididae, Ptychopteridae,
Tanyderidae, and some Tipulidae (Antocha, Rhabdomastix, Dicranota, Hexatoma,
Limnophila, Tipula)
(V)
Ephemeroptera: all members, except: Siphlonuridae, and some Ephemeridae
(Hexagenia)
(VI) Megaloptera: all
members, except: Chauliodes
(VII)
Odonata: Aeshnidae, Calopterygidae, Cordulegastridae, Gomphidae, some
Coenagrionidae (Argia, Chromagrion, Amphiagrion), some Libellulidae
(Perithemis), and some Corduliidae (Epitheca, Helocordulia,
Neurocordulia)
(VIII) Plecoptera:
all members
(IX) Trichoptera: all
members, except: Molannidae, some Leptoceridae (Nectopsyche,
Triaenodes), and some Limnephilidae (Ironoquia, Limnephilus,
Hesperophylax)
(X) Oligochaetes:
Branchiobdellidae, Lumbriculidae, Sparganophilidae, some Tubificidae (subfamily
Naidinae, Ilyodrilus, Rhyacodrilus, Varichaetadrilus), and some Lumbricidae
(Eiseniella tetraedra only).
(iii) The presence of any indigenous fish
species, other than the Mosquitofish (Gambusia), documented under normal
weather conditions, is also a primary indicator that the watercourse is a
stream, and constitutes support of the requisite aquatic life.
(iv) There are conditions in which a stream
may be dry for a period of weeks or even months, but supports multiple
populations of lotic aquatic organisms or fish at other times during a year. In
such conditions, an investigator could appropriately determine that there is
sufficient water on an annual basis to support such populations even though
there were not any present on a particular date. In addition, man-made
pollution or other water quality issues may preclude support of these
organisms. Therefore, the absence of lotic aquatic organisms at the time of the
investigation cannot be the sole basis for a determination that a watercourse
meets the fourth element of the definition. When multiple populations of lotic
aquatic organisms or fish cannot be documented to occur in a watercourse, then
the investigator must consider the hydrologic and biologic factors referred to
as secondary indicators in these rules and the Guidance to make a hydrologic
determination.
(v) Under normal
weather conditions, if the investigator documents the absence of water due to
naturally occurring conditions in a watercourse between February 1 and April
15, then the investigator can conclude the watercourse is unable to support
fish or multiple populations of obligate lotic aquatic organisms whose life
cycle includes an aquatic phase of at least two months and is therefore a wet
weather conveyance.
